The browning is the most common sign that something is wrong with the botanical Thuja. You can find out which diseases are behind them here.
The botanical Thuja is a very hardy plant, making it a very popular hedging plant in home gardens. You can tell whether the thuja is he althy by the color of its leaves. If the leaves are a rich green and the small leaves that grow back are also green, you can assume that the plant is he althy. If the thuja has a problem, whether it's a disease or an infestation by pests, its leaves turn brown. The brown color should not be confused with the natural brown color of some species in winter. However, if the botanical thuja gets brown leaves in summer, one can assume that the plant is not he althy. There are several pests that can damage the plant and the thuja is not safe from diseases either.
What diseases and pests are there?
Although the botanical thuja is a very hardy plant and rarely affected by diseases and pests, there are some negative influences. Basically, the pests can be divided into the following categories:
- Fungus Diseases
- Diseases caused by pests
- Root rot and stem rot
- external influences
Fungal diseases of botanical thuja
Fungal diseases are the most common diseases of botanical Thuja. Since most types of thuja turn brown in winter, the fungal attack is often not immediately noticeable. There are basically four major types of mushrooms:
- Pestalotiopsis funerea
- Didymascella thujina
- Kabatina thujae
- Armillaria mellea
❶ Pestalotiopsis funerea
This fungus triggers the well-known Pestalotia dieback. This is the most common disease of botanical thuja, but it is very easy to spot. The characteristic clinical picture shows a brown discoloration that emanates from the outer tips of the leaves. The coloring spreads further and further until it has reached the shoots. Black-brown spots form on the shoots, which are typically round and about the size of aare pinheads. This fungus prefers soft, already damaged tissues because the fungus is a weakness parasite that can cause significant damage to the plant.
❷ Didymascella thujina
This fungus is known to cause needle and scale tan. Mainly older leaf scales turn brown. Initially, only isolated brown spots can be seen. These spread further and further until later spore deposits are recognizable. These turn black and the shoot dies off quickly.
❸ Kabatina thujae
This fungus mainly attacks the young leaves and the soft tips of the shoots. Here you can see black spore beds located on brown leaves. This fungus can be distinguished from Didymascella thujina by the sharp, black border to the he althy leaves.
❹ Armillaria mellea
This fungus is also known as Honey fungus. Here the plants die very quickly and can hardly be saved. The fungus triggers a typical white mycelium that is very easily recognizable. The network is deposited between bark and wood and is therefore so dangerous for the botanical thuja. It literally destroys the plant from the core.
What to do if you have fungus?
The first measure should be a radical cutback. The affected shoots should be pruned generously, whereby the old wood is not cut. If the plant is affected by Armillaria mellea, the use of fungicides can be helpful. However, this is only the case if the disease is detected early. Fungal infestation is usually only noticed very late and the plants no longer recover, despite fungicides. Then the whole thuja has to be dug up and new bushes have to be planted in the ground. Fungal infestation is common when the soil is too acidic and the plant is deficient in magnesium and calcium. Therefore, when setting the thuja, care should be taken to ensure that the soil is loose, nutrient-rich. This is an efficient way to prevent fungal diseases.
Diseases caused by pests
Although the botanical Thuja is very hardy, some pests can have a major impact on its he alth. While there are few pests that attack botanical thuja, these animals can do a lot of damage. The enemies of the thuja hedge are the thuja miner moth, the bark beetle and the spider mite. They trigger different symptoms.
➀ The thuja miner moth
The thuja miner moth is the most common pest that can cause massive damage to the thuja. The moth has already beenIntroduced from North America in 1970 and is often found in native gardens. The clinical picture that causes it is quite easy to recognize. The moth primarily infests the driving tips. These turn brown. If the driving tip is not treated, complete calcification can occur. The thuja miner moth mainly strikes in spring. It eats into the scales of the thuja. If you look at the tips of the shoots, you can see the typical drilling and drilling holes of the moth. The moth eats through the shoots and thus builds its tunnels, where the larvae, which are about 4 mm small, are located.
» Treatment:
In order to get rid of the thuja minion moth effectively, the infested shoot tips must be cut radically. There is no other method of treatment. Please dispose of the cut shoots outside of the garden, because the moth starts to fly in July and can spread very quickly.
➁ The bark beetle
The bark beetle makes small boreholes through which it builds its tunnels. The adult beetle, which is about 2-3 mm in size, enters the plant and lays its eggs there. You can recognize the seat of the bark beetle by small thickenings on the branches. The larvae hatch and eat their way through the shoots. This leads to the ultimate death of the drive. The bark beetle mainly attacks weak plants and usually occurs after an extremely dry season.
» Treatment:
Even when infested by the bark beetle, only radical pruning can lead to success. The affected branches and shoots must be removed. The twigs should not be disposed of in your own compost, because the bark beetle can also spread very quickly.
➂ The Thuja Spider Mite
The thuja spider mite rarely infests the botanical thuja. The infestation occurs mainly in dry and warm weather. The spider mite sucks on the leaf scales. This creates speckles of yellow or silver color. Since the spider mite is only a few millimeters in size, it is often overlooked and the clinical picture is mistaken for a nutrient deficiency. Webs can often be seen on the affected shoot tips.
» Treatment:
If the botanical Thuja is infested with spider mites and you have identified them, treatment is very simple. The small animals are very sensitive to all fertilizers. You can therefore treat the thuja with a pest-free spray. This is he althy for the plant itself, but kills all adults and larvae as well.
Things to knowfor prophylaxis against vermin
If you already had the problem that the thuja was attacked by pests, you can use a pest-free spray for prophylaxis at the end of June. These sprays have the advantage of working throughout the system. This means that the active ingredient penetrates the interior of the plant and is distributed throughout the plant. Stems, shoots and leaves absorb the active ingredient and are therefore robust against pests. Most pests suck or eat from the plant. They absorb the active ingredient and die.
Diseases caused by external influences
The botanical thuja also often suffers from diseases due to external influences. Drought, but also moisture and s alt can damage Thuja.
■ Wetness
If the botanical thuja is constantly in the wet soil, stem and root rot will occur. This can be recognized by the white coating. The thuja likes it moist, but the trunk and roots should be dry. Once the blight has attacked the trunk and roots, the plant can no longer be saved. Before a new plant is planted, the soil must be replaced generously.
■ Drought
If it is over 30°C in summer, the botanical Thuja must be watered regularly. If the plant suffers from a lack of water, the leaves turn brown and the plant dies. Even in winter, the water evaporates and the thuja has to be watered. This should only be done on frost-free days, because the water should never freeze on the shoots.
■ S alt
The road s alt in winter is an extreme stress factor for the botanical Thuja. Therefore, make sure that the road s alt does not get to the trunk and roots of the plant. If this is the case, the plant needs to be watered well to dilute the s alt.
Conclusion
The botanical thuja is a very robust plant that has few enemies. However, if the plant is attacked by a pest or fungus, you must act quickly. This ensures that the diseases cannot spread and that other plants are spared. A radical cut can in any case bring the desired effect and the Thuja can recover quickly. If you observe your plants, changes in the shoots can be recognized very quickly. This is the prerequisite for a long life of the botanical thuja.